The present invention generally relates to an automobile fuel intake system and, more particularly, to a fuel intake system for a multi-cylinder internal combustion engine for closing one of at least two passages leading to respective engine cylinders during a particular operating condition of the engine to allow the whole amount of air-fuel mixture to be introduced into the corresponding engine cylinder through the other of the passages, thereby to improve the efficiency of combustion occurring in such corresponding engine cylinder and to minimize the amount of noxious unburned components of the exhaust gases to be emitted to the atmosphere.
U.S. Pat. No. 2,114,655, patented on Apr. 19, 1938, discloses an automobile fuel intake system comprising a carburetor for combining fuel with air to form a combustible mixture to be supplied into a plurality of engine cylinders and including a throttle valve for controlling the rate of delivery of the combustible air-fuel mixture to the engine cylinders, an intake manifold having a common inlet, communicated to the carburetor, and branch passages equal in number to and communicated respectively to the engine cylinders, and shutter valves each in the form of a butterfly valve operatively positioned within certain of the branch passages for, during a particular operating condition of the engine, for example, during shifting, coasting, braking and like operations, closing such certain of the branch passages, the combustible air-fuel mixture being, however, introduced into all of the engine cylinders during the time that the engine is pulling a load.
A system similar to that described above is also disclosed in the U.S. Pat. No. 3,578,116, patented on May 11, 1971.
A feature of interest in terms of present invention, which is common to the both of the above mentioned U.S. patents, resides in that a negative pressure developed within the intake system at a position upstream of the shutter valves with respect to the direction of flow of the combustible air-fuel mixture towards the engine cylinders is utilized as an operating signal necessary for the shutter valves to be selectively closed and opened depending upon the engine operating condition. Specifically, the shutter valves are so associated and so arranged as to be closed and opened respectively when the negative pressure upstream of the shutter valves exceeds a predetermined value and when it falls below the predetermined value. In this arrangement, the shutter valves tend to undergo a surging motion, i.e., repeated cycles of opening and closing, in such a manner that, when the negative pressure upstream of the shutter valves exceeds the predetermined value and the shutter valves are therefore closed, the closure of the shutter valves results in reduction of the negative pressure upstream of the shutter valves to such an extent as to cause it to fall below the predetermined value, thereby opening the shutter valves, which in turn results in increase of the negative pressure upstream of the shutter valves to such an extent as to exceed the predetermined value. The surging motion tends to adversely affect the performance of the engine and, therefore, should be removed.
According to the Japanese Utility Model Publication No. 52-18342, published on Apr. 25, 1977, the invention of which has been assigned to the assignee of the present invention, there is disclosed a carburetor for combining fuel with air to provide a combustible mixture which is to be supplied into at least two engine cylinders through respective intake passages, throttle valves equal in number to the number of the intake passages and operatively positioned therein for controlling the rate of delivery of the combustible mixture to the respective engine cylinders, a connecting passage communicating between the intake passages at a position downstream of any one of the throttle valves with respect to the direction of flow of the combustible mixture towards the engine cylinders, and a shutter valve operatively positioned within one of the intake passages at a position downstream of and proximate to the connecting passage such that, when the shutter valve is held in position to close such one intake passage during a particular engine operating condition, namely, when the throttle valves are substantially closed and the engine is operated at a high speed, a portion of the combustible mixture flowing through such one intake passage can be introduced into the other of the intake passages.
In this Japanese publication, for operating the shutter valve which is normally biased by a spring element to open such one intake passage, an electromagnetic actuator is employed in combination with series-connected switches, one used to detect the position of the throttle valve and the other used to detect the speed of rotation of the engine. However, this device does not utilize a negative pressure upstream of the shutter valve for operating the latter such as employed in the earlier mentioned U.S. patents, although there is no substantial possibility of the occurrance of the surging motion of the shutter valve because of the employment of a mechanical linkage system between the shutter valve and the electromagnetic actuator.
Although the above mentioned Japanese publication describes the possible utilization of the negative pressure in combination with a diaphragm valve, instead of the electric current including the electromagnetic actuator, for operating the shutter valve, it has failed to disclose a specific fluid circuit through which the requisite negative pressure is drawn and a specific arrangement of the diaphragm valve in relation to the fluid circuit.
If one can conceive of the possibility of utilization of the negative pressure downstream of the shutter valve and merely applies it to the device of the above mentioned Japanese publication in place of the fluid circuit including the electromagnetic actuator, there would be a critical problem. In other words, although there is no problem where the negative pressure downstream of the shutter valve is utilized to close the shutter valve when it exceeds the predetermined value with the throttle valve opened, reduction of the negative pressure downstream of the shutter valve will no longer take place during the opening of the throttle valve once the shutter valve has been closed and, therefore, the once-closed shutter valve will become incapable of being opened.